The present invention relates to a charged particle beam technique for irradiating a sample with a charged particle beam, to observe, analyze, and process the sample.
An apparatus for a charged particle beam for irradiating a sample with a charged particle beam and observing, analyzing, and processing the sample is widely used. In the case where a sample contains an insulating material, when the surface of the sample is scanned with a charged particle beam, the surface of the sample may be charged. The charging disturbs observation, analysis, and processing due to drift of an emitted beam and decrease in a discharge amount of secondary particles. Consequently, a method of preventing the charging is important.
Conventional charging preventing methods include a method of preventing charging by irradiating the surface of a sample with a charged particle beam, a method of making charges escape by forming a conductive layer on the surface of a sample by irradiation of an ultraviolet ray or charged particle beam, a method of making charges escape by covering the surface of a sample with a conductive film, and a method of making charges escape by using conductive foil, conductive paste or a conduction terminal.
As a method of preventing charging by irradiation of a charged particle beam, there is, as prior art 1, xe2x80x9ccharged particle beam processing apparatus and method (Japanese Patent Application Laid-Open (JP-A) No. 8-138617)xe2x80x9d. The prior art 1 discloses an apparatus and method for detecting secondary electrons from the surface of a sample without extracting electrons emitted from an electron gun for preventing charging by a secondary electron detector by disposing the nozzle-shaped tip of the electron gun near the surface of the sample at the time of preventing charging of the sample with an ion beam, by using an electron beam.
The method of making charges escape by forming a conductive layer on the surface of a sample by irradiation with an ultraviolet ray or charged particle beam includes, as prior art 2, xe2x80x9csecondary electron image detecting method and apparatus, and processing method and apparatus using focusing charged particle beam (JP-A-11-154479)xe2x80x9d and xe2x80x9ccharged particle beam processing apparatus and method (JP-A-8-138617)xe2x80x9d. The prior art 2 discloses an apparatus and method realizing processing of 1.0 xcexcm or less in such a manner that charging is stably avoided irrespective of the state and kind of a sample, a secondary electron image of the sample is detected at high resolution in a real time manner, and observation of the pattern of the sample, positioning of the focused charged particle beam, and the like are realized with high accuracy by the method of inducing a conductive layer and making charges escape by irradiating a region including a focused charged particle beam irradiation region on the surface of a sample with a positive ion beam.
As the method of covering the surface of a sample with a conductive film, there is, as prior art 3, xe2x80x9cmethod of manufacturing conductive resist film and semiconductor device (JP-A-7-74076)xe2x80x9d. The prior art 3 discloses a method of suppressing charging as much as possible by a method of forming a conductive film under a resin film which is sensitive to charged particles and a method of exposing a pattern with high accuracy while reducing a charged particle beam curved irradiation phenomenon.
The method of making charges escape by a conductive terminal includes, as prior art 4, xe2x80x9csample charging eliminating apparatus (JP-A-2000-173525)xe2x80x9d. The prior art 4 discloses an apparatus preventing hindrances to observation, analysis, and processing due to a charging phenomenon and realizing a high-sensitivity, high-resolution, and high-precision work by making charges generated during the process of observation, analysis, and processing escape via an earth line by allowing a terminal to come into contact with the periphery of at least 180 degrees of an observation, analysis, and processing region by a remote control.
The method of capturing charges by a conductive probe includes, as prior art 5, xe2x80x9cmicropattern measuring apparatus (JP-A-7-94562)xe2x80x9d. The prior art 5 discloses a micropattern measuring apparatus which prevents a charge-up phenomenon in such a manner that negative charges generated by an electron beam are captured either by directly contact of a probe with a micropattern or by applying a positive voltage of 5000V to a probe from a position apart from the micropattern by 30 xcexcm.
According to the prior arts, by the method of covering the surface of a sample with a conductive substance or making a conductive substance come into contact with the surface of a sample, the method of irradiating the surface of a sample with a charged particle beam, or the like, charging which occurs at the time of irradiating the sample with a charged particle beam is eliminated.
According to the charging preventing methods of the prior arts 1 and 2, if the irradiation amount of an electron or ion beam used for preventing charging does not coincide with that of the charged particle beam used for observation, analysis, and processing, charging occurs. In this case, to improve resolution of an observed image by improving the precision of an irradiation position of a charged particle beam and to improve contrast of an observation image by increase in an emission amount of secondary electrons generated by irradiation of the charged particle beam, the irradiation amount of an electron or ion beam has to be controlled by means for detecting a charging preventing condition by using a reference. Further, control of the irradiation amount by the charging preventing condition detecting means requires experience of the operator.
Further, secondary electrons emitted by irradiation with an electron or ion beam are detected by a secondary electron detector. At this time, the secondary electrons overlap with secondary electrons emitted from the surface of a sample irradiated with the charged particle beam, so that the secondary electrons emitted by the irradiation of the electron or ion beam deteriorate an observation image very much. In order to suppress an emission amount of the secondary electrons emitted by the irradiation of the electron or ion beam, the irradiation amount has to be regulated. When a charging amount of the surface of a sample is large, the charging preventing method by irradiation of an electron or ion beam is not effective.
Generally, secondary electrons generated by the irradiation of a charged particle beam are emitted 10 to 100 times as much as secondary ions. Consequently, the resolution of an observation image based on a secondary electron signal is higher than that of an observation image based on secondary ions. However, in the case of emitting an electron or ion beam in order to prevent charging, due to generation of secondary electrons, the resolution of an observation image based on the secondary electron signals deteriorates more than that of an observation image based on secondary ions. Therefore, in the apparatus for a charged particle beam, a secondary ion detector is widely used.
In the charging preventing method of the prior art 3, a coating with a conductive layer is formed on the surface of a sample. When the surface of a sample is covered, however, the structure of the surface cannot be observed with a charged particle beam, and a problem occurs in determination of a position of observation, analysis, and processing with a charged particle beam. Further, in order to avoid contamination of a sample, the charging preventing film formed on the surface of the sample has to be removed after observation, analysis, and processing with the charged particle beam.
According to the method of making charges escape by the conductive terminal disclosed in the prior art 4, the terminal has to be made come into contact with the periphery of at least 180 degrees of the region of observation, analysis, and processing by a remote control. By making the terminal come into contact with the periphery of at least 180 degrees of the region of observation, analysis, and processing, it becomes difficult to recognize the contact of the terminal and, simultaneously, positioning precision in the state where the terminal is in contact deteriorates. Further, a region wider than the observation, analysis, and processing region irradiated with the charged particle beam is contaminated by the contact of the terminal.
According to the method of capturing charges by the conductive probe disclosed in the prior art 5, when the probe is in contact, the probe hides a part of a micropattern, so that the micropattern cannot be observed. In the case where the probe is not in contact, an observation image is distorted by a strong electric field generated when charged electrons are captured by the probe.
In the case of fabricating a sample by using a charged particle beam without employing the charging preventing method, the operator has to perform observation, analysis, and processing by relying on a drifting observation image. Since operations and setting are visually recognized, a work of performing the observation, analysis, and processing without using the charging preventing method requires skill. When the operator fails in the processing, the sample may be destroyed. When the operator fails in a probe operation, the sample or the tip of the probe may be destroyed.
The above methods have subjects such as reduction in contamination of a sample, lessening of a work of covering the surface of a sample with the conductive substance or making the conductive substance contact with the surface, reduction in charges newly generated by irradiation of the surface of a sample with a charged particle beam and an influence of the terminal onto observation, analysis, and processing using secondary electrons, and elimination of a skill to directly extract a sample piece from a sample.
The present invention has been achieved in consideration of the above and its object is to provide a very reliable method of preventing charging without requiring experience or skills to suppress charging in the surface of a sample and to provide an apparatus for a charged particle beam having generally excellent analysis and sample fabricating efficiency.
The present invention provides, as means achieving the object, a technique based on novel finding such that charging which occurs when a sample is irradiated with a charged particle beam (ion beam, electron beam, or the like) is controlled by an electrode for preventing charging provided adjacent to or in contact with the irradiated area.
Even when the electrode for preventing charging and the irradiated area are electrically insulated from each other, when the area is irradiated with a charged particle beam, a current induction occurs between the charged irradiated area and the electrode for preventing charging for the following reason. By efficiently extracting secondary particles emitted from the surface of the sample charged by the irradiation of the charged particle beam by the electrode for preventing charging, a current induction occurs between the electrode for preventing charging and the irradiated area. When the electrode for preventing charging is provided within, for example, 300 xcexcm from the irradiated area or in contact with the irradiated area, by the irradiation of the charged particle beam, a current flows between the charged irradiated area and the electrode for preventing charging.
When the operator performs observation, analysis, processing, and probe operation of high precision, the interval between the electrode for preventing charging and the irradiated area has to be further reduced. As the interval is reduced, the charging voltage decreases by the induced current or the generated current between the electrode and the irradiated area, and an electric field near the irradiated area generated by the charging can be confined in a narrower space. As a result, the irradiation position of the charged particle beam in the surface of the insulating sample can be controlled with position precision of about 1/50 times of the interval. Simultaneously, a secondary particle detection amount in a secondary particle detector is not influenced by charging, so that a clear observation image can be obtained.
Representative configuration examples of a method of preventing charging and an apparatus for a charged particle beam using the method of the invention realizing observation, analysis, processing, and probe operation of high precision by using the technique of preventing charging will be described hereinbelow.
First, the invention provides a method of preventing charging, including the steps of irradiating a sample mounted on a sample holder with a charged particle beam emitted from a charged particle beam source, and applying a predetermined voltage to an electrode for preventing charging disposed near a surface of the sample holder to generate an induced current between the electrode for preventing charging and an irradiated area in which charging occurs in the sample, thereby executing a control of preventing the charging without contact with the sample.
The invention also provides a method of preventing charging, including the steps of irradiating a sample mounted on a sample holder with a charged particle beam emitted from a charged particle beam source, applying a predetermined voltage to an electrode for preventing charging disposed near a surface of the sample holder, and making the electrode come into contact with the sample to generate a current between the electrode for preventing charging and an irradiated area in which charging occurs in the sample, thereby executing a control of preventing the charging.
The invention provides an apparatus for a charged particle beam, having: a charged particle source; a charged particle optical system for focusing and deflecting a charged particle beam emitted from the charged particle source; a detector for detecting secondary particles emitted from a sample irradiated with the charged particle beam; and a sample holder on which the sample is mounted, the apparatus including: an electrode for preventing charging which is provided so as to be movable with respect to the surface of the sample holder; and a controller for the electrode for preventing charging, for controlling a voltage to be applied to the electrode for preventing charging and the movement, wherein a control for preventing the charging is performed by generating an induced current or a current between an irradiated area in the sample, which is irradiated with the charged particle beam, and the electrode for preventing charging.
The invention also provides an apparatus for a charged particle beam, having: a charged particle source; a lens for focusing a charged particle beam emitted from the charged particle source; a deflector; a detector for detecting secondary particles emitted from a sample irradiated with the charged particle beam; a sample holder for holding the sample, and a sample position controller for controlling the position of the sample holder, the apparatus being provided with: a first electrode which is provided between a charged particle beam irradiated area in the sample and the lens so as to be movable with respect to the sample and which generates an induced current or a current between the first electrode and the charged particle beam irradiated area; an electrode controller controlling the first electrode, and driving independent of the sample holder position controller; and a second electrode driving independent of the sample holder position controller and generating a current between the second electrode and the charged particle beam irradiated area, wherein a control of preventing charging in the charged particle beam irradiated area which is charged is performed by using the first and second electrodes.